1. Field of the Invention
The present invention relates to a stent, a manufacturing method thereof and indwelling method thereof, the stent being capable of opening intracorporeal lacuna for a long time for treatment of stricture of blood-vascular and non-blood-vascular system such as bile duct and digestive tract, and obstructive lesion, which has attracted attention in the field of so-called IVR (Interventional Radiology) treatment.
2. Description of Related Art
Broadly speaking, metal stents are classified into two types: one is set around a balloon catheter to be expanded and indwelled by balloon expansion; the other has expansibility by itself such as Z-stent and xe2x80x9cwall-stentxe2x80x9d. Stainless steel, shape memory alloy or the like are used as material of the stent.
In order to indwell a stent having expansibility by itself, the stent such as the Z-stent is pushed out of a catheter to be released and indwelled, or a stent is set around a catheter-shaped core and covered with a sheath and is released when the sheath portion is drawn backward.
However, since the position of such stents cannot be corrected once expanded in the intracorporeal lacuna, additional stents are generally indwelled, which makes treatment difficult, increases burden on patients and deteriorates safety of the treatment.
In view of the above, a stent using bidirectional shape memory alloy is known (Japanese Patent Publication Hei 3-51430).
The stent uses bidirectional shape memory alloy wire composed of Nixe2x80x94Ti type, Cuxe2x80x94Alxe2x80x94Ni type and Cuxe2x80x94Znxe2x80x94Al type alloy formed in a shape capable of expanding and contracting in the diametral direction thereof, more specifically, a spiral shape, a spiral cylindrical shape, a cylindrically braided shape, or a pipe shape. The stent keeps a form expanded in diametral direction thereof at or around body temperature (35xc2x0 C. to 37xc2x0 C., for example) and becomes a form contracts in the diametral direction at a temperature substantially lower than body temperature (15xc2x0 C. to 20xc2x0 C., for example).
However, though the diameter of the stent using the bidirectional shape memory alloy expands and contracts in accordance with temperature change, the diameter change is small.
According to the description in the above Japanese ""340 publication, the stent having a Nixe2x80x94Ti type bidirectional shape memory alloy (containing approximately 51 atomic weight % of Ni) of 0.04 mm thick and 1 mm width has an inner diameter of approximately 2.0 mm at body temperature and contracts to approximately 1.4 mm of inner diameter at a temperature of not more than 15xc2x0 C., exhibiting only approximately 0.6 mm of difference.
Accordingly, the stent cannot be indwelled into the intracorporeal lacuna and cannot be moved while firmly wound around a catheter.
Further, the stent disclosed in the Japanese Publication is not suited for practical use.
In other words, when deformation in two directions occurs, desired deformation cannot be securely obtained unless the material is suitably selected and thermal treatment is appropriately conducted, which results in difficulty in accurately controlling the shape and generated force.
Accordingly, the above-described stent using the bidirectional shape memory alloy has not been made into practical use at present.
To solve the above-described problems, an object of the present invention is to provide a stent and manufacturing method and indwelling method thereof, the stent capable of increasing change of diameter etc. enlarging and contracting in accordance with temperature change and capable of being configured into any shape at higher temperature and lower temperature, the stent therefore being suitably selected and used in different intracorporeal lacuna diameter, so that indwelling to the intracorporeal lacuna and position correction after indwelling can be facilitated to enhance safety and reduce burden for the patient.
In order to achieve the above object, a stent according to the present invention is arranged as follows.
A stent according to the present invention has a hollow cylindrical body made of a plurality of filament bodies of Tixe2x80x94Ni alloy having excessive Ni, the hollow cylindrical body memorizing a first ashape during a lower-temperature shape memorizing process and a second shape during a higher-temperature shape memorizing process and being deformable between the first shape and the second shape in accordance with temperature change.
In other words, the stent is formed into the hollow cylindrical body by braiding the plurality of filament bodies, where the hollow cylindrical body is deformable into mutually different first and second shape. The lower-temperature shape memorizing process is conducted in the first shape condition and the higher-temperature shape memorizing process is conducted in the second shape, so that reversible deformation is possible between the two shapes in accordance with temperature change, in which the hollow body approaches the first shape in lower temperature and approaches the second shape in higher temperature.
The deforming shape may be any shape between the first shape and the second shape. In other words, between the first shape and the second shape, reversible deformation within an area from a shape similar to the first shape and slightly close to the second shape to a shape similar to the second shape and slightly close to the first shape, may also be possible.
The Tixe2x80x94Ni alloy includes at least Ti and Ni. However, other chemical elements may be contained therein.
According to the present invention, since the hollow cylindrical body formed by braiding the plurality of filament bodies of Nixe2x80x94Ti-alloy having excessive Ni experiences the lower-temperature shape memorizing process in the first shape and the higher-temperature shape memorizing process in the second shape to memorize both shapes, the hollow cylindrical body can change the shape thereof from the first shape to the second shape or from the second shape to the first shape, in accordance with temperature change.
Therefore, when the first shape and the second shape are set to have a smaller diameter in lower-temperature and a larger diameter in higher-temperature to secure enough difference between respective cylinder diameter, the diameters change enlarging and contracting in accordance with temperature change can be increased relative to the conventional stent and the enlarged and contracted shapes can be formed in any desired shape.
Further, the first shape and the second shape can be set in any configuration. For instance, the change in accordance with temperature may not be a change in diametral dimension but may be a change in axial dimension. For instance, the first shape may be linear tube and the second shape may be curved or bent cylindrical shape such as J-shape, L-shape, C-shape, U-shape and S-shape.
Further, the hollow cylindrical may not be a consecutive cylinder having constant diameter, but either the first shape or the second shape may be a tapered tube shape having a gradually changing diameter dimension. As described below, only the end portion of the cylinder may be enlarged in tapered manner.
In the stent according to the present invention, the lower-temperature shape memorizing process may preferably be a solution thermal treatment and the higher-temperature shape memorizing process may preferably be a constraint aging thermal treatment.
Accordingly, the shape memorization in the first shape and the second shape can be further securely conducted, thereby accurately controlling the respective shapes and generated force for increasing change between respective shapes.
In the stent according to the present invention, the first shape preferably has smaller cylinder diameter than the second shape.
According to the above, the stent can substitute for the above-described conventional stent. Since the diametral change in accordance with temperature change can be increased relative to the conventional stent, the stent can be freely selected and applied to intracorporeal lacuna having different diameter, so that indwelling to the intracorporeal lacuna and correction of the indwelled position can be easily conducted, thereby improving patient safety and reducing burden of the.
In the stent according to the present invention, crossed portions of the filament bodies may preferably be fixed only at both ends of the hollow cylindrical body.
Accordingly, since the crossed portions of the filament bodies are fixed on both ends of the hollow cylindrical body and the crossed portions of the other than both of ends are set free, the change in longitudinal direction can be reduced even when the diameter of the hollow cylindrical body is enlarged and contracted in accordance with temperature change. In other words, since the crossed portions of the filament bodies are fixed only on both ends of the hollow cylindrical body, the longitudinal change can be reduced while allowing a large diameter change (enlarging and contracting) in accordance with temperature change, thereby reducing indwelling error in indwelling the stent into the intracorporeal lacuna.
In the stent according to the present invention, the first shape of the hollow cylindrical body may preferably have a smaller diameter than the second shape and the second shape may preferably have a larger diameter at both opening ends than an intermediate portion thereof.
In conventional stents, after being inserted in the intracorporeal lacuna in a small-diameter condition of a lower-temperature, the stent is deformed with large-diameter condition a higher-temperature. In the deformation, though desired diameter enlargement can be obtained at the intermediate portion, it is known by experience that sufficient diameter enlargement cannot be obtained at both opening ends, which may cause disadvantage of humor flow toward the outer circumference of the stent and generation of thrombus etc. at that time.
On other hand, when the both opening ends are enlarged to have a larger diameter than the intermediate portion with enlarged condition, both opening ends enlarge to the same diameter as the intermediate portion or larger, thereby preventing humor flow into the outer circumference of the stent. Further, since the end portion of the stent firmly catches the wall of intracorporeal lacuna, unnecessary movement of the stent can be prevented.
In the stent according to the present invention, one or more of the plurality of filament bodies may preferably be made of gold or tantalum.
Accordingly, since the hollow cylindrical body includes the filament body of gold or tantalum photographable under fluoroscopy of roentgen rays, shadowing effect by X-rays can be expected, so that the position of the stent can be checked by roentgen rays when the stent is indwelled or withdrawn from the body. Accordingly, safe operation can be secured.
In the stent according to the present invention, the Tixe2x80x94Ni alloy may preferably contain Co or Cu.
Accordingly, transformation temperature and deformation rate can be changed by the added elements, thereby being capable of selectively producing an expansive soft stent or an expansive rigid stent in accordance with usage.
Manufacturing methods of the stent according to the present invention includes the following arrangement.
A manufacturing method of a stent according to the present invention includes the steps of: braiding a plurality of filament bodies of Tixe2x80x94Ni alloy of excessive Ni to form a hollow cylindrical body deformable into mutually different first and second shape; memorizing a lower-temperature shape for memorizing the first shape to the hollow cylindrical body as a lower-temperature shape; and memorizing a higher-temperature shape for memorizing the second shape to the hollow cylindrical body as a higher-temperature shape.
Accordingly, the first shape as the lower-temperature shape can be memorized to the hollow cylindrical body during the lower-temperature shape memorizing process and the second shape as the higher-temperature shape can be memorized during the higher-temperature shape memorizing process. Therefore, the first shape and the second shape can be securely memorized, thereby increasing shape change, enlargement and contraction for example, in accordance with temperature change and changing the hollow cylindrical body into any desired shape. Accordingly, the stent can be selectively freely applied to the intracorporeal lacuna having different diameter, thereby facilitating indwelling into the body and corrected at the indwelled position, so that patient safety can be improved and patients discomfort reduced.
In the manufacturing method of the stent according to the present invention, a solution thermal treatment may preferably be conducted during the lower-temperature shape memorizing step while keeping the hollow cylindrical body in the first shape, and an aging thermal treatment may preferably be conducted during the higher-temperature shape memorizing step while binding the hollow cylindrical body in the second shape.
According to the above arrangement, shape memorization of the first shape and the second shape can be further securely conducted, so that respective shapes and generated force can be accurately controlled and the change between the respective shapes can be further magnified.
An indwelling method of a stent according to the present invention includes the following steps.
An indwelling method of a stent according to the present invention includes the steps of: providing a stent having a first shape of lower-temperature with a larger the cylinder diameter than cylindrical diameter of a second shape of higher-temperature; accommodating the stent into a sheath after making it thinner than the cylinder diameter of the first shape; inserting a distal end of the sheath adjacent to the indwelling position of intracorporeal lacuna; and inserting a rod into the sheath and pushing out the stent in the sheath to indwell the stent in the intracorporeal lacuna.
Accordingly, since the diameter change enlarging and contracting in accordance with temperature change of the stent itself is large and the stent has approximately one ninth of the elastic modulus relative to stainless steel in martensitic structure, the stent can be accommodated in a thin sheath after applying outside force to make the cylinder diameter thinner. Therefore, the treatment can be facilitated as compared to a method in which the stent is held on an outside of distal portion of the catheter to be inserted into the intracorporeal lacuna.